Fixed cutter rotary drill bits carry a plurality of cutting elements. Each cutting element typically comprises a thin table of a superhard material bonded to a substrate of a less hard material. The superhard material may for instance be a polycrystalline diamond or boron cubic nitride and the substrate a cobalt cemented tungsten carbide. Such cutting elements are typically of generally cylindrical shape, with the table of superhard material forming a circular end of the cutting element. An edge between the circular end and the curved peripheral wall forms a cutting edge of the cutting element.
During drilling, the cutting edge of the table cuts the rock, shearing and penetrating into the rock formation. A sharp edge is beneficial to cutting efficiency, but is also prone to wear due to the high stresses that a sharp edge may experience in cutting through a tough geologic formation. Damage or wear to the cutting edge reduces the cutter life, and also the cutting efficiency and the rate of penetration into the rock formation. As the cutting edge is damaged, the rig-floor response is often to increase weight on bit to compensate, which quickly results in further degradation and ultimately catastrophic failure of the worn element.
If initial chipping of the diamond table cutting edge can be eliminated, both the life of a cutter and the cutting efficiency thereof can be significantly improved.
One known method for reducing wear of a diamond table cutting edge is to bevel or chamfer the edge. U.S. Pat. No. 4,343,180 and U.S. Pat. No. 5,979,579 teach the use of single chamfer on the periphery of a polycrystalline diamond compact (PDC) cutter. Although such a chamfer increases durability of the cutter, it also reduces cutting efficiency and penetration rate compared with a sharp cutter under the same loading conditions, particularly for large chamfers.
U.S. Pat. No. 7,316,279 discloses a sharp edged cylindrical cutting element with axial grooves in the edge of the diamond table. U.S. Pat. No. 8,037,951 discloses a cutting element with chamfered cutting edge and a substantially flat front face, wherein the cutting element is profiled with features in the cutting face so as to vary the depth of chamfer along the cutting edge.
US2011/0301036 describes a cutting element in which an end face of the cutting element is of profiled form. U.S. Pat. No. 6,220,376 also show cutting elements with profiled end faces.
A cutting element is desirable that combines the cutting efficiency of a sharp edge with the enhanced durability obtainable by a chamfered edge.